The experience with the ELISA test for detection of antibodies to Strongyloides stercoralis continues to increase. The antigen is an aqueous supernate extracted from filariform (L3) larvae, grown in fecal cultures. The parasite is obtained from patients encountered at the NIH, or from Patas monkeys infected with the human parasite. About 90 percent of parasitologically proven cases have antibody at a 1:8 serum dilution or greater. The same antigen, as well as a secretion-excretion(metabolic) antigen from the L3's, also stimulate histamine relese when exposed to peripheral basophils from infected individuals. The Patas monkey has been found to be susceptible to infection with human S. stercoralis. The Patas monkey appears to be a model for the hyper-infection syndrome, a sometime fatal complication of steroid treatment or other immuno-suppression of human infection with this parasite.